30/06/2010 EQS_57125_Free cyanides_v3.doc
Free Cyanides
1 Chemical identity
Cyanides are a group of chemical compounds characterised by occurrence of the association of a carbon and a nitrogen atom (CN). These compounds occur as free cyanides (HCN and CN-), simple associations to cyanides as NaCN and KCN, metal-cyanides complexes (e.g. iron and cyanides) and organic complexes (nitriles and glucosides).
Cyanides mainly occur in waters as free cyanides, mostly hydrogen cyanide (HCN) which represents the main toxic form with cyanide ion CN- (US-EPA, 1984).
In this document [HCN] refers to hydrogen cyanide, [NaCN] refers to sodium cyanide and [KCN] refers to potassium cyanide.
Common name / CyanideChemical name (IUPAC) / Cyanide
Synonym(s) / Free cyanide
Chemical class (when available/relevant) / Inorganic compound
CAS number / 57-12-5
EC number / -
Molecular formula / CN-
Molecular structure /
Molecular weight (g.mol-1)
Common name / Hydrogen cyanide
Chemical name (IUPAC) / Hydrogen cyanide
Synonym(s) / Formonitrile
Chemical class (when available/relevant) / -
CAS number / 74-90-8
EC number (EINECS) / 200-821-6
Molecular formula / HCN
Molecular structure / H+
Molecular weight (g.mol-1) / 27.03
Common name / Sodium cyanide
Chemical name (IUPAC) / Sodium cyanide
Synonym(s) / -
Chemical class (when available/relevant)
CAS number / 143-33-9
EC number (EINECS) / 205-599-4
Molecular formula / NaCN
Molecular structure /
Molecular weight (g.mol-1) / 49
Common name / Potassium cyanide
Chemical name (IUPAC) / Potassium cyanide
Synonym(s) / -
Chemical class (when available/relevant)
CAS number / 151-50-8
EC number (EINECS) / 205-792-3
Molecular formula / KCN
Molecular structure /
Molecular weight (g.mol-1) / 65.11
2 Existing evaluations and Regulatory information
LegislationAnnex III EQS Dir. (2008/105/EC) / Included as “Free cyanide” (CAS 57-12-5)
Existing Substances Reg. (793/93/EC) / No
Pesticides(91/414/EEC) / [HCN] and [NaCN] Notified, Not included in Annex I (Dec. 2004/129/EC)
[KCN] Not notified
Biocides (98/8/EC) / [HCN] Notified, (PT8 Wood preservatives, PT14 Rodenticides, PT18 Insecticides) – under evaluation.
[KCN] and [NaCN] Not notified
PBT substances / Not investigated
Substances of Very High Concern (1907/2006/EC) / No
POPs (Stockholm convention) / No
Other relevant chemical regulation (veterinary products, medicament, ...) / No
Endocrine disrupter
Groshart and Okkerman, 2000 / - Investigated, not categorised
Petersen et al., 2007 / - Excluded from the evaluation because insufficient data
3 Proposed Quality Standards (QS)
3.1 Environmental Quality Standard (EQS)
QSwater_eco for protection of pelagic organisms is 0.22 µg.l-1 for freshwater, respectively 0.022 µg.l-1 for marine waters and is deemed the “critical QS” for derivation of an Environmental Quality Standard.
Data are available on 3 trophic levels for both acute and chronic ecotoxicity and a statistical extrapolation of the results via a SSD was done, applying assessment factors of 5 and 50 for derivation of QSwater_eco, and MAC-QS for freshwater and saltwater, respectively. Significant differences between freshwater and marine species cannot be demonstrated from the information available.
Value / CommentsProposed AA-EQS for [freshwater] [µg.l-1]
Proposed AA-EQS in [marine waters] [µg.l-1] / 0.22
0.022 / Critical QS is QSwater eco
See section 5
Proposed MAC-EQS for [freshwater] [µg.l-1]
Proposed MAC-EQS for [saltwater] [µg.l-1] / 3
0.3 / See section 5.1
3.2 Specific Quality Standard (QS)
Protection objective[1] / Unit / Value / CommentsPelagic community (freshwater) / [µg.l-1] / 0.22 / See section 5.1
Pelagic community (marine water) / [µg.l-1] / 0.022
Benthic community (freshwater) / [µg.kg-1 dw] / Not triggered / See section 5.1
Benthic community (marine) / [µg.kg-1 dw] / Not triggered
Predators (secondary poisoning) / [µg.kg-1biota ww] / Not triggered / See section 5.2
[µg.l-1] / Not triggered
Human health via consumption of fishery products / [µg.kg-1biota ww] / Not triggered / See section 5.3
[µg.l-1] / Not triggered
Human health via consumption of water / [µg.l-1] / 50
4 Environmental Behaviour
4.1 Environmental distribution
Master referenceWater solubility (mg.l-1) / [HCN] Miscible at 25°C / HSDB, 2000
[NaCN] 48104 at 10°C
82104 at 35°C
[KCN] 72104 at 25°C / ATSDR, 2006
Volatilisation
Vapour pressure (Pa) / [HCN] 83103 at 20°C
99103 at 25°C / ATSDR, 2006
Daubert and Danner, 1989
[NaCN] 101 at 800°C / ATSDR, 2006
[KCN] 2.410-11 at 25°C (estimated) / US-EPA, 2008
Henry's Law constant (Pa.m3.mol-1) / [HCN] 13.5 / Gaffney et al., 1987
[NaCN] 1.210-14 (estimated) / US-EPA, 2008
[KCN] 1.610-15 (estimated)
Dissociation / [HCN] 9.2
Solutions containing cyanides compounds (KCN, NaCN) dissociate in HCN in water, at neutral and acidic pH. / ATSDR, 2006
Adsorption / The range 2.4 – 1000 is used for derivation of QS
Organic carbon – water partition coefficient (KOC) / [HCN] 15.1 (experimental) / US-EPA, 2008
[NaCN] 2.41 (estimated)
[KCN] 2.41 (estimated)
Sediment – water partition coefficient(Ksed -water) / [HCN] 3 / Calculated from KOC
[NaCN] 1.3
[KCN] 1.3
Bioaccumulation / The BCF value of 0.5 is used for derivation of QSbiota secpois because tests were made on NaCN, but for conversion between matrices (necessary for derivation of the EQS), maximal value of 1.6 is used. Thus, BMF1 = BMF2 = 1 E.C., 2009.
Octanol-water partition coefficient (Log Kow) / [HCN] 0.66 / ATSDR, 2006
[NaCN] 0.44
[KCN] -1.69 (estimated) / US-EPA, 2008
BCF fish (calculated) / [HCN] 0.7 – 1.6 / ATSDR, 2006
Calculated from KOW
[NaCN] 0.5
4.2 Abiotic and Biotic degradations
Master referenceHydrolysis / In most of natural waters, temperature is too low and pH too neutral (4 – 9) for hydrolysis of cyanide and its compounds to occur. / Boening and Chew, 1999
Photolysis / Photodegradation can lead to breakdown of complexes and release of free cyanides in clear waters. HCN compounds and free cyanides ions seem to resist to photolysis when exposed to natural light. In clear waters / Boening and Chew, 1999
ATSDR, 1997
Biodegradation / Biodegradation is the main degradation process of cyanides in surface waters.
DT50, rivers = 10 – 24 d (data of low reliability) / ATSDR, 1997
5 effects and Quality Standards
Cyanide mode of action is similar in all organisms. The cyanide ion reacts with the central metal ion of metallo-enzymes to form cyanide complexes thus rendering those enzymes non-functional. The primary target in cytochrome oxidases is the central iron ion (Fe3+). Examples of other, cyanide-sensitive enzyme systems are catalase and other peroxidases, myoglobin, nitrite and nitrate reductase and nitrogenase (Solomonson and Spehar, 1981) and CO2 reductase (Thauer et al., 1973). These enzymatic disturbances result in respiratory depression and can inhibit aerobic metabolism.
Free cyanide ions can also pass through the gill membrane causing biochemical disturbances, possibly resulting in tissue damage and nervous system effects. This may result in sublethal effects such as erratic or lethargic behaviour, impairment of swimming and effects on metabolism.
Sublethally, cyanide has also been shown to increase brain dopamine levels in fish. This inhibits the production of gonadotrophins, which may result in negative effects on fish reproduction (Murgatroyd et al., 1998 in Sorokin et al., 2007).
5.1 Acute and chronic aquatic ecotoxicity
The different forms of cyanide have different chemical properties and hence different degrees of toxicity to aquatic organisms. HCN and CN- are the principal toxic forms of free cyanides, the former being more toxic because it is able to cross the biological membranes.
Therefore, toxicity data from HCN, CN- and its salts (KCN and NaCN) were taken on board thereafter and all results below are expressed as mg HCN.l-1.
ACUTE EFFECTS / Klimmisch code / Master referenceAlgae & aquatic plants
(mg.l-1) / Freshwater / Chlorococcales sp. / 24h, static
EC50, physiology= 0.045 / 2
ECETOC, 2007 / Krebs, 1991
Marine / Nitzschia closterium / 72h
EC50: 0.057 [NaCN] / 1 – 2
Verbruggen et al., 2001
Sorokin et al., 2007
ECETOC, 2007 / Pablo et al., 1997
Invertebrates
(mg.l-1) / Freshwater / Daphnia pulex / 24 – 96h
LC50= 0.1 (mean values of 11 data ranging 0.001 – 0.42) / 1 – 2
(ECETOC, 2007) / Lowest data:
Cairns et al., 1978
Marine / Cancer irroratus / 96h
LC50: 0.0042 [KCN] / 1 – 2
Sorokin et al., 2007 / Johns and Gentile (1981)
4
(ECETOC, 2007)
Acartia clausi / 96h
LC50 = 0.03 / 1 – 2
Verbruggen et al., 2001 / Eisler, 1991
ECETOC, 2007 / Brix et al., 2000
Sediment / No information available
Fish
(mg.l-1) / Freshwater / Salmo salar / 24h
LC50: 0.023 [KCN] / 1 – 2
Sorokin et al., 2007 / Alabaster et al., 1983
Oncorhynchus mykiss / 96h
LC50: 0.028 [unknown form] / 1 – 2
Sorokin et al., 2007 / Kovacs and Leduc, 1982
Oncorhynchus mykiss / 96h
LC50: 0.043 [KCN] / 1 – 2
Sorokin et al., 2007 / McGeachy and Leduc, 1988
Marine / Menidia menidia / 96h
LC50: 0.059 / 4, supporting info
(Sorokin et al., 2007) / Berry and Gardner, 1985
Sediment / No information available
(1) reported as Eisler, 1991 in RIVM report. Actually referring to Lee, 1976 in US-EPA, 1980 in Eisler, 1991.
CHRONIC EFFECTS / Valid according to / Master referenceAlgae & aquatic plants
(mg.l-1) / Freshwater / Scenedesmus quadricauda / 8d
NOECpopulation = 0.012 / 2
(ECETOC, 2007) / Bringmann and Kühn, 1978
Marine / Champia parvula / 14d
NOECgrowth= 0.0039 / 2
(ECETOC, 2007) / Steele and Thursby, 1983
Invertebrates
(mg.l-1) / Freshwater / Gammarus pseudolimnaeus / 98d
NOECgrowth= 0.0039 [HCN] / 2
(ECETOC, 2007) / Oseid and Smith, 1979
Marine / Mytilus galloprovincialis /48h, larvae
NOEClarvae growth = 0.0032 / 2
(ECETOC, 2007) / Pavicic and Pihlar, 1982
Sediment / No information available
Fish
(mg.l-1) / Freshwater / Salvelinus fontinalis / 144d
NOECreproduction= 0.0057 / 1 – 2
Verbruggen et al., 2001 / Koenst et al., 1977
Salvelinus fontinalis / 144d
NOECreproduction= 0.0054 / 2
(ECETOC, 2007)
Lepomis macrochirus / 289d
LOEC reproduction= 0.005
Extrapolation to NOECrepro= 0.001 / 2
(ECETOC, 2007) / Kimball et al., 1978
Marine / Cyprinodon variegatus / 28d
NOECgrowth = 0.029 / 4, cited by US-EPA, 2003(1)
(ECETOC, 2007) / Schimmel, 1981
Sediment / No information available
(1) www.epa.gov/ecotox
The Draft Guidance Document on EQS derivation (E.C., 2009) states that “in principle, ecotoxicity data for freshwater and saltwater organisms should be pooled for organic compounds, if certain criteria are met” and that “the presumption that for organic compounds saltwater and freshwater data may be pooled must be tested, except where a lack of data makes a statistical analysis unworkable.”
This is the case for cyanides. In fact, there are too few data (either freshwater or saltwater) to perform a “meaningful statistical comparison” and no further indications of “a difference in sensitivity between freshwater vs saltwater organisms”, the mode of action (cf. first paragraph of part 7.) not being information allowing differentiating between the two media.
Therefore, in this case, the data sets may be combined for QS derivation according to the Guidance Document on EQS derivation (E.C., 2009).
ECETOC has published a report (ECETOC, 2007[2]) in which an SSD based on acute crustaceans data is available. On the one hand, this SSD does not address all taxa together while cyanides present a non-specific mode of action but on the other hand, crustaceans represent the most sensitive taxa as regards acute effects (increased sensitivity of Daphnia pulex and Cancer irroratus). Therefore, the SSD led on crustaceans data resulting in a HC5 of 15 µg.l-1 is proposed for MAC-QS derivation.
Species sensitivity distribution for acute effects on crustaceans (geometric means of all LC50 or EC50 values per species)
According to EQS TGD (E.C., 2010), an assessment factor of 10 should be applied to derive the MAC-QS. However, the dataset available is substantial and most crustaceans families are covered. Therefore, assessment factors of 5 and 50 are deemed conservative to derive the MAC-QSfreshwater, eco, respectively the MAC-QSsaltwater, eco.
In the same report (ECETOC, 2007), long term data are analysed for which SSDs are presented for freshwater and saltwater organisms together, as well as for freshwater organisms only: these SSDs led on the most reliable data (Klimisch code 1 – 2) result in an HC5 of 1.1 µg.l-1 and 1.4 µg.l-1, respectively. As no significant difference can be demonstrated between freshwater and saltwater sensitivities, it is deemed more conservative to base the QS derivation on the freshwater and saltwater SSD including a higher number of species and for which HC5 is 1.1 µg.l-1.
Species sensitivity distribution of sublethal NOECs for freshwater and saltwater species
According to EQS TGD (E.C., 2010), an assessment factor of 1 to 5 should be applied to derive the AA-QSwater, eco. Given that some TGD EQS requirements are not fulfilled, i.e. in the taxonomic groups represented in the SSD, insects are missing as well as macrophytes and an 8th taxonomic group. Therefore, it seems reliable to apply assessment factors of 5 and 50 to this HC5 to derive AA-QSfreshwater, eco, respectively the AA-QSsaltwater, eco.
Tentative QSwaterAssessment factor method / Relevant study for derivation of QS / AF / Tentative QS
MACfreshwater, eco / SSD – HC5 = 0.015 mg.l-1 / 5 / 3 µg.l-1
MACmarine water, eco / 50 / 0.3 µg.l-1
AA-QSfreshwater, eco / SSD – HC5 = 0.0011 mg.l-1 / 5 / 0.22 µg.l-1
AA-QSmarine water, eco / 50 / 0.0022 µg.l-1
AA-QSfreshwater, sed. / Triggers not met (log Koc < 3) according to TGD EQS (E.C., 2009)
AA-QSmarine water, sed. / Triggers not met (log Koc < 3) according to TGD EQS (E.C., 2009)
5.2 Secondary poisoning
According to the Draft Guidance Document on EQS derivation (E.C., 2010), this substance does not trigger the bioaccumulation criteria given the low values of log KOW (-1.69 – 0.66), the low value of BCF (0.5 – 1.6) and that the LOEC reported for oral toxicity of mammals is quite high (60 mg.kg-1feed ww, see below).
Secondary poisoning of top predators / Master referenceMammalian oral toxicity / Miniature pigs / Oral / 24 wk / Neurobehavioural and biochemical effects
LOAEL[3] = 1.2 mg.kg-1bw.d-1
LOEC = 60 mg.kg-1feed ww (CF = 50) / Jackson et al., 1985
in Jackson, 1988
in WHO, 2003
Avian oral toxicity / No available information
Tentative QSbiota secpois / Relevant study for derivation of QS / AF / Tentative QS
Biota / Not triggered
5.3 Human health
According to the Draft Guidance Document on EQS derivation (E.C., 2010), this substance does not trigger the bioaccumulation criteria given the low values of log KOW (-1.69 – 0.66), the low value of BCF (0.5 – 1.6). Moreover the substance is classified only for its acute effects. Hence, protection of human health from consumption of fishery product is not deemed relevant.